1. Field of the Invention
This invention relates to an ultrasonic wave device for vehicle which is mounted on the vehicle so as to detect a vehicle height or the like relative to the road surface by a reflected wave from the ultrasonic wave sensor, and more particularly to an icing preventive device for an ultrasonic wave transmitting and receiving unit for automatically preventing icing during operation of a heater operating circuit.
2. Description of the Prior Art
In recent years, various types of sensors have been developed as the vehicle shows a tendency toward high performance, and more particularly as a sensor to be installed outside of the vehicle body. For example, a vehicle retracting sensor for sensing an obstacle may be placed rearward of the vehicle, a so-called back-sonar and a supersonic wave sensor may be used in a so-called supersonic suspension developed to improve a good ride and a driving stability under the most appropriate control of measurement of variation in vehicle height and dampening force of the shock absorber in response to the condition in the road surface such as a bad road surface and the like during the running of the vehicle.
However, the vehicle is not always operated under the most preferable environmental condition. For example, it frequently occurs that the vehicle runs on a snowy road during the winter season, wherein the transmitting and receiving unit shows a decreased height against the road due to an adhesion of snow to the supersonic wave transmitting and receiving unit or icing and normal operation of the unit is frequently hindered.
Due to this fact, in order to prevent such a disadvantage as described above, a device for preventing generation of dewdrops or icing has been developed, in which for example an electrically conductive vibration-proof rubber is arranged in the vibrating element of the supersonic wave transmitting and receiving unit and heated.
However, according to the prior art as described above, the melting operation for the snow or ice adhered to the supersonic wave transmitting and receiving unit is not performed in response to a decreasing in function of the transmitting and receiving unit caused by snow or icing; rather, the heater is merely heated and energized with a manual switch or the heater is heated or energized in response to a sensing of low temperature with a temperature sensor. Thus, the heater may sometimes be energized when the snow or ice is not adhered to the supersonic wave transmitting and receiving unit or even upon completion of the melting of the snow or icing and it may generate a disadvantage that useless electric power is consumed. Further, since the operation for preventing icing was not rational and was troublesome, a delay in operation occurred, resulting in that it was not possible to provide a proper prevention of icing in the supersonic wave transmitting and receiving unit. Further, when the operation of the manual switch was performed manually, a useless operation was present and further showed some problems that the manual switch itself deteriorated and wore out.